Generally, a high-voltage pulse of at least 20 kV must be applied between the electrodes in order to initiate a discharge in a high-pressure discharge lamp.
To generate this high-voltage pulse, a large transformer and high-voltage resistant electronic components must be used in the lighting device, adversely affecting lighting device miniaturization and cost savings.
Also, noise occurring when the high-voltage pulse is generated causes operational errors and failure in the lighting device and surrounding electronic circuitry.
The prior art proposes decreasing the lamp breakdown voltage by mounting a proximity conductor to the outside of the bulb, as with the high-pressure mercury lamp described for example in Japanese Patent Application Publication No. 2001-43831, thereby decreasing the height of the high-voltage pulse generated by the lighting device.
FIG. 10 shows the structure of a high-pressure mercury lamp 500 according to conventional technology. As shown in the diagram, conventional high-pressure mercury lamp 500 includes a bulb 550 having a light emitting part 501, sealing parts 502 and 503 provided one at each end of light emitting part 501, and a wound portion 521 and a lead portion 522 of the proximity conductor, the light emitting part 501 having a pair of electrodes 504 and 505 disposed with a predetermined interval therebetween and a discharge space 512 formed therein.
Electrodes 504 and 505, which are electrically connected to external lead wires 508 and 509 via molybdenum foils 506 and 507 sealed respectively by sealing parts 502 and 503, are structured to receive power supply from an external source via molybdenum foils 506 and 507 and external lead wires 508 and 509.
Note that mercury and a rare gas are enclosed within light emitting part 501 at respective predetermined amounts.
Wound portion 521 of the proximity conductor is formed from a single-turn closed loop disposed so as to encircle a vicinity of the boundary between light emitting part 501 and sealing part 502. Wound portion 521 is electrically connected, via lead portion 522, to external lead wire 509 extending from the other end of sealing part 503.
With this structure, a 350 V DC voltage or an AC voltage of less than 50 Hz, for example, is firstly applied to electrodes 504 and 505 as a pre-discharge voltage, over which a high-voltage pulse considerably higher than the pre-discharge voltage is applied to initiate the discharge.
With this high-pressure mercury lamp according to conventional technology, electric fields are generated between electrode 504 and electrode 505, wound portion 521, and lead portion 522, respectively, due to the application of the high-voltage pulse between electrodes 504 and 505, resulting in a strong electric field concentrating in a vicinity of electrode 504. This concentrated electric field enables the discharge to be initiated with a relatively low high-voltage pulse.
However, even with this method disclosed in Japanese Patent Application Publication No. 2001-43831, a fairly large transformer and high-voltage resistant electronic components are required as before, meaning that the above demands for lighting device miniaturization and cost savings are not met. Also, the noise that occurs when generating the high-voltage pulse is not greatly decreased.
The present invention, devised in view of the above problems, aims to provide a high-pressure discharge lamp, a lighting method and lighting device for a high-pressure discharge lamp, a high-pressure discharge lamp device, and a lamp unit, image display device and headlight device that sufficiently decrease the height of a high-voltage pulse generated by a lighting device to allow for lighting device miniaturization, cost savings and noise reduction.